The high risks of building high rises

One Dalton will be Boston’s tallest residential building, almost eye-to-eye with the Prudential. If constructing something that tall in the middle of a busy urban hub sounds tricky, complex, and fraught with risks and challenges, that’s because it is.

By Doug Bailey| September 25, 2017

Darren Messina insists to anyone who asks that he sleeps soundly. But he’d be forgiven for fits of tossing and turning. He is, after all, managing the details, logistics, scheduling, and risks that come with building what will be the tallest residential high-rise building in New England.

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When it’s done, do you know how Messina will learn if the building is leaning or tilting even a tiny fraction of an inch, because of high winds or any ground shifts? Satellites, soaring hundreds of miles off in space, will tell him so.

Messina, the executive vice president of Cambridge-based Carpenter & Company, is overseeing the construction of One Dalton, a 742-ft. Back Bay luxury hotel and 160-unit condominium tower. As the city’s third tallest building, just eight feet shorter than the Prudential Tower and roughly 80 feet shorter than 200 Clarendon Street (commonly known as the John Hancock building), it will permanently alter the Boston skyline.

And it will give its residents a vantage point no one else has ever had in Boston.

“You’ll have people living way up there,” Messina says. “You don’t want them to get the feeling of any drift or movement, and certainly not any leaning.”

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Though One Dalton’s size is modest by some standards (at 742 feet, it would be eclipsed by nearly four dozen New York City skyscrapers, including at least eight that are more than 1,000 feet tall), the increasing complexity and risks, as the deadly fire at a London high-rise in June revealed, are enormous to insurance companies and risk consulting services.

“In a downtown Boston site like that, it’s a very tight site, not a lot of space to make an error,” said Giles Boucher, the senior vice president of claims and risk control for Cross Insurance. He said if a worker high above kicks off a wrench, and the proper netting isn’t in place, the consequences could be severe.

And lately, he said, he’s seen more and more horror stories about cranes collapsing on huge projects. “A crane sitting on top and hoisting materials up all day long, it defies the laws of gravity,” he said.

One story vs. 61 stories

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Listening to Messina calmly describe how the massive One Dalton project comes together, it sounds as if constructing 61 stories is no different than building one; you just have to do it 61 times.

Of course, that’s not really true.

Building something this tall, Messina has to think about the impact of natural catastrophes: earthquakes, flooding, hurricanes, and blizzards. The threat posed by wind loads and fire; the varying wind speeds between ground and higher levels; the elastic shortening of building elements as the weight of the building increases; pumping and placing concrete and other materials like windows at high levels; and, perhaps most important, making sure the building stays level, truly vertical, and doesn’t sway much.

And there is one particularly unique problem for managing risk at One Dalton: It sits on a small triangular footprint.

“My wife is an architect and she looked at it before we started working on it and she said, ‘No way. It can’t be done,’” Messina said. “It’s a 14,000 square-foot building on a 15,000 square-foot site. It’s tight.”

To build One Dalton, engineers had to bore 165 feet into the bedrock and then about 20 feet into the rock on the sides to install sockets for heavy bracings in the foundation. Then, as the building goes up, a giant belt truss is installed to mitigate movement.

As a result, extra care has to be taken to insure the construction doesn’t disrupt or weaken nearby structures or foundations. Pedestrians and traffic need to continue to move very close to where workers are installing giant glass windows and concrete towers, and it all adds risk to the overall construction. Anyone who remembers what happened in the early 1970s when giant glass windows began falling out of the Hancock Tower and crashing on to the sidewalk can relate. Snow removal becomes an added issue as several feet of snow on the top of a high-rise during construction cannot be simply pushed off the side to the street below and must be slowly melted and drained.

Swaying in the breeze

How will they tell if the building is still standing perfectly straight? Geosynchronous satellites, of course, which are orbiting satellites that return to the same position in space each day and trace a path in the sky. Such precision is critical, because if the building veers by just a fraction of an inch, the elevators could scrape the walls as they try to move, just one example of potential impact.

Swaying is only one of the concerns Messina ticks off when he talks about the risks of building a high rise. One slight variance or any unanticipated event could halt the entire project or, worse, inject a dangerous unforeseen risk into the completed building.

He also has to manage tons of concrete trucked outside the city, as the timing from the moment it leaves the plant to the time it arrives on site has to be carefully tracked because the cement will weaken if not poured within a specific timeframe. Thousands of pounds of concrete would have to be discarded because of a small traffic jam.

“It makes the logistical planning that much more critical,” Messina said. “There’s no real staging area where we can lay materials, so everything has to be carefully planned.”

And then there’s the issue of worker safety, as construction crews install floors, windows, and other framing components while in the open air 700 feet overhead, navigating around enormous cranes and swinging beams. Dangerous as it sounds, innovations in modern construction techniques have significantly lessened the risks to workers themselves.

“We build a ‘cocoon’ that encases the workers but also protects people below,” says Robert Sullivan, vice president and project executive at AECOM Tishman, which has managed some of the largest and most complex developments in the U.S. “So after initial construction they are completely enclosed for the duration and it’s self-jacking, so as they move up the cocoon moves up with them.”

Typically, this “cocoon” is at least three decks, Sullivan explains, with little elevators at the corners for moving material between the various decks.

“It provides a good, stable, and efficient work environment that could be on ground level or could be 70 stories in the air,” he said.

Perhaps the greatest innovation that helps lower risk is advanced computer technology. Construction engineers today can “build” entire buildings down to the last digital detail long before actually breaking ground. That digital replica can signal in advance where difficulties and conflicts will arise, and they can be resolved before a shovel goes into the ground.

“Having a 3-D visual of the project really helps the builders,” says Rachel Hildebrand at Suffolk Construction, the manager of building information modeling and virtual design. “The contractors, the subcontractors, and everyone else has access to the data and visuals in the field in real time, right on site, so they can see where risks and tolerances are cropping up and share it with whomever they need.”

And then design changes can be made to the computerized schematics instantly, Hildebrand said, allowing engineers to immediately see what effects those changes will have and whether they will involve greater risk evaluation.

One big factor: The safety of the residents. “There are obvious challenges with tall buildings,” said Boucher of Cross Insurance. “You can’t run out of the building on the second floor, you need a carefully thought out evacuation plan.” And that plan can’t just be for people who can walk and run, he said. It has to prepare for people in wheelchairs or other impairments.

None of these challenges, however, is slowing down the momentum in tall building construction. Plans for buildings taller than One Dalton have already been proposed in Boston but so far none approved.

“Things can fall off a building during construction, everything from hoisting sections into place or workers dropping a tool,” said Fran McCormack, director of risk control services at Cross Insurance. “Boston in general has become more sophisticated when it comes to safety. Obviously there is always a moral desire to be safe. But there are also financial incentives.”

Currently the world’s tallest building, the Burj Khalifa in Dubai, stands at 2,717 feet. But construction has begun for an even taller building, the Jeddah Tower, in Saudi Arabia, which, when it opens in 2019, will be at least 3,280 feet tall. Construction experts and risk insurance services say they expect within the next 10 years, someone will build a mile-high building, a thought that really does keep risk analysts and fire and safety officials up at night.